Ultrastructure of glomerular basement membrane by quick-freeze and deep-etch methods.

The glomerular basement membrane of rat kidneys were three-dimensionally observed by quick-freeze and deep-etch replica methods at high resolution. The middle layer (lamina densa) was composed of 6 to 10 nm fibrils which formed a meshwork structure. The space between the fibrils had polygonal shape. The average long dimension of the space between fibrils was 17 nm and the short one was 13 nm. At the outer layer (lamina rara externa), fibrils connected podocytes perpendicularly with the meshwork of the middle layer. At the inner layer (lamina rara interna), similar perpendicular fibrils also connected endothelial cells with the meshwork of the middle layer. This is the first report to visualize the three-dimensional meshwork structure of the middle layer (the lamina densa) in situ. The function of anchoring podocytes to the lamina densa was suggested in the perpendicularly arranged fibrils of the outer layer. The quick-freeze and deep-etch method is useful in analyzing filamentous ultrastructure in glomeruli, and will be applied to clarifying pathological ultrastructure in kidney diseases.